A Group III nitride semiconductor material such as a gallium indium nitride mixed crystal (GaXIn1-XN: 0<x<1) has been used conventionally for constituting a light-emitting layer of a light-emitting diode (abbr.: LED) emitting blue or green short wavelength light or a laser diode (abbr.: LD) (see, for example, JP-B No. 55-3834). Aluminum gallium nitride (composition formula AlXGa1-XN: 0≦X≦1) has been used as a material used for constituting a light-emitting layer having a quantum well structure of a near-ultraviolet or ultraviolet LED (see, for example, JP-A No. 2001-60719).
A Group III nitride semiconductor LED comprising a Group III nitride semiconductor layer as a light-emitting layer is combined with an LED comprising a light-emitting layer constituted of a nitride semiconductor layer except a Group III nitride semiconductor layer, for example, a Group III-V nitride semiconductor layer and thereby is used for constituting a multicolor emission LED. For example, blue and green LEDs respectively comprising, as light-emitting layers, GaXIn1-XN layers with different indium (In) compositions (=1−X) and a red LED comprising an aluminum gallium arsenide mixed crystal (AlGaAs) as a light-emitting layer are assembled and thereby a light-emitting device which emits light of each color of R (red), G (green), and B (blue) or emits white light by mixing these colors is produced (see, for example, JP-A No. 7-335942).
As another type of conventional white LED, there is an LED of a two-wavelength light-emitting type utilizing a technique of forming respective light-emitting layers emitting lights in a relation of complementary colors on a single substrate. For example, a light-emitting layer having a multiple quantum well structure, which comprises five GaXIn1-XN (0≦X≦1) well layers emitting blue light, and a light-emitting layer having a multiple quantum well structure emitting yellow light and comprising ten pairs of AlInP/AlGaInP are respectively formed on the same substrate, and two lights with different colors and wavelengths (for example, blue and yellow lights) emitted respectively from the light-emitting layers are mixed, whereby a two-wavelength light-emitting white LED is provided (see, for example, JP-A No. 2001-257379).
However, when the conventional LED which emits a plurality of lights with different wavelengths (multiwavelength emission) is constituted, it is necessary to separately provide light-emitting layers formed of a Group III-V compound semiconductor material suitable for emitting each color. For example, when an LED emitting each color of RGB is produced, as described above, light-emitting layers respectively emitting R (red), G (green), and B (blue) are required to be formed of different Group III-V compound semiconductor materials. Namely, LED which easily provides multiwavelength emission using a single light-emitting layer independently constituted of a Group III nitride semiconductor layer could not have been produced.
The present invention has been proposed in view of the above circumstances and an object thereof is to provide a Group III nitride semiconductor light-emitting device which can easily emit multiwavelength light with a simple constitution, using a single light-emitting layer independently constituted of a Group III nitride semiconductor layer.